Messages in this thread | | | Date | Mon, 18 Jan 2021 11:14:55 +0100 | From | Jessica Yu <> | Subject | Re: [PATCH v3] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols |
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+++ Fangrui Song [15/01/21 11:52 -0800]: >clang-12 -fno-pic (since >https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6) >can emit `call __stack_chk_fail@PLT` instead of `call __stack_chk_fail` >on x86. The two forms should have identical behaviors on x86-64 but the >former causes GNU as<2.37 to produce an unreferenced undefined symbol >_GLOBAL_OFFSET_TABLE_. > >(On x86-32, there is an R_386_PC32 vs R_386_PLT32 difference but the >linker behavior is identical as far as Linux kernel is concerned.) > >Simply ignore _GLOBAL_OFFSET_TABLE_ for now, like what >scripts/mod/modpost.c:ignore_undef_symbol does. This also fixes the >problem for gcc/clang -fpie and -fpic, which may emit `call foo@PLT` for >external function calls on x86. > >Note: ld -z defs and dynamic loaders do not error for unreferenced >undefined symbols so the module loader is reading too much. If we ever >need to ignore more symbols, the code should be refactored to ignore >unreferenced symbols. > >Reported-by: Marco Elver <elver@google.com> >Link: https://github.com/ClangBuiltLinux/linux/issues/1250 >Signed-off-by: Fangrui Song <maskray@google.com> >Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> >Tested-by: Marco Elver <elver@google.com> >Cc: <stable@vger.kernel.org> > >--- >Changes in v2: >* Fix Marco's email address >* Add a function ignore_undef_symbol similar to scripts/mod/modpost.c:ignore_undef_symbol >--- >Changes in v3: >* Fix the style of a multi-line comment. >* Use static bool ignore_undef_symbol.
Patch has been queued up on modules-next:
https://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git/commit/?h=modules-next&id=ebfac7b778fac8b0e8e92ec91d0b055f046b4604
Thanks!
Jessica
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